codeconsole commented on code in PR #15732:
URL: https://github.com/apache/grails-core/pull/15732#discussion_r3408456657
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grails-web-core/src/main/groovy/org/grails/web/servlet/HttpServletRequestExtension.groovy:
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@@ -251,4 +252,26 @@ class HttpServletRequestExtension {
static Date date(HttpServletRequest request, String name,
Collection<String> formats) {
TypeConverters.toDate(request.getAttribute(name), formats)
}
+ /**
+ * Null-safe, typed read of an attribute. Returns the attribute when it is
an
+ * instance of {@code type}; otherwise {@code null}. No coercion is
attempted —
+ * use the named converters ({@code string}, {@code int}, ...) for type
conversion.
+ */
+ static <T> T getAttribute(HttpServletRequest request, String name,
Class<T> type) {
+ if (type == null) {
+ throw new IllegalArgumentException('type must not be null - use
getAttribute(name) for an untyped read')
+ }
+ Object value = request.getAttribute(name)
+ Class<T> resolvedType = (Class<T>)
ClassUtils.resolvePrimitiveIfNecessary(type)
+ resolvedType.isInstance(value) ? resolvedType.cast(value) : null
Review Comment:
`type.isInstance(value)` is true when `value` *is-a* `type`, including when
`type` is a supertype/interface of the value's concrete class. That's the
primary use case for these reads:
```groovy
// stored value is a concrete DefaultCsrfToken; caller requests the interface
CsrfToken token = request.getAttribute('_csrf', CsrfToken)
```
`value.class.isAssignableFrom(type)` inverts the relationship — it asks "is
`type` the same as or a *subclass* of the value's class", i.e.
`DefaultCsrfToken.isAssignableFrom(CsrfToken)`, which is `false` — so it would
return `null` for every request-by-interface. The supertype-match case is
covered by the spec (`getAttribute('principal', CharSequence)` for a
`StringBuilder` value).
The `isAssignableFrom` equivalent of the current check would be
`type.isAssignableFrom(value.class)` (with a null guard);
`type.isInstance(value)` just expresses that directly and is null-safe.
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